Conventionally, an optical pickup section used in an optical disk apparatus has an optical construction in which semiconductor laser light is concentrated on and applied to a disk by a lens, reflected light has its light intensity modulated according to the signal written on the disk and this reflected light is further made incident on a light-receiving device (or a circuit-integrated type light-receiving device in which the light-receiving device and a transistor for processing an electric signal taken out of this light-receiving device are integrated on an identical substrate). This light-receiving device (or the circuit-integrated type light-receiving device) employed in this optical pickup section also detects a focus signal and a servo signal according to the shapes of a plurality of light rays applied to and reflected on the disk besides the detection of the data signal written on the disk. Then, control is executed so that light is accurately applied to the disk, in which the data signal is written, on the basis of the detected focus signal and servo signal.
Then, the optical pickup section employs a segmented type light-receiving device constructed of a plurality of pn junctions that can receive a plurality of light rays (refer to Japanese Laid-open Publication No. H9-213920). A dielectric film is formed on the light-receiving device surface, on which light is incident, of the segmented type light-receiving device in order to control the reflectance on the device surface. When a single-layer oxide film is employed as this dielectric film construction, a condition of λ/4n (n represents the refractive index of the oxide film, and λ represents the wavelength of light) of an optimum film thickness is satisfied, and the oxide film thickness is 70 nm with respect to, for example, light of a wavelength of 400 nm. Moreover, a multilayer structure, which has a low reflectance with respect to the wavelength to be used, is also employed as the aforementioned dielectric film construction.
As shown in FIG. 20, in the case where, for example, two light-receiving sections are formed by providing n-type semiconductor layers 901 and 902 on a p-type semiconductor layer 900 (there is shown none of the electrode leads, the interlayer films and so on of the n-type semiconductor layer and the p-type semiconductor layer), electric charges are accumulated in a dielectric film 903. Therefore, an N-type inversion layer 904 is formed by the inversion of the conductive type in the surface of the p-type semiconductor layer 900, and the two light-receiving sections are disadvantageously connected together by this n-type inversion layer 904. Consequently, there is a problem that signals cannot be individually taken out of the two light-receiving sections and the device does not function as a segmented type light-receiving device. The problem of the segmented type light-receiving device easily occurs particularly when the concentration of the p-type semiconductor layer on which the n-type semiconductor layer is provided is reduced to improve the frequency characteristic determined by a CR time constant by reducing the capacitance of the pn junction of the segmented type light-receiving device.